This disclosure relates generally to hydraulic circuits for optimizing the handling of paper rolls or other objects by means of a lift truck-mounted load clamp capable of automatically applying load-weight-responsive variable hydraulic load-clamping force.
U.S. Pat. No. 6,454,511 discloses a prior electrical system for load weight-responsive hydraulic control of load-clamping force by electrically sensing load weight and automatically limiting maximum hydraulic load clamping force by a pressure relief valve variably controlled by an electrical controller in response to the sensed load weight.
US Patent Application Publication No. 2010/0089704 discloses a simpler mechanical type of system which does not require an electrical controller, and nevertheless is capable of automatically applying load-weight-responsive variable hydraulic load-clamping force. However this latter load weight-dependent clamping system was not previously considered usable in conjunction with a hydraulic clamping cylinder having more than a single extensible stage, because each additional successive stage of such a cylinder during cylinder extension has a progressively reduced pressure area resulting in a progressively reduced clamping force, which might cause the clamp to drop a clamped load.